Band 33, Heft 1

When molten plastic is extruded from a die, it sometimes collects on the open face of the die. Known as die drool, this phenomenon costs plastics manufacturers by requiring die cleaning. This has been attributed to many causes, but none of these has led to an equation for the drool rate. In this work, we provide an exact analytical solution for the drool rate, and we base this solution on a postulate of a cohesive slip layer near the die walls. We thus attribute die drool to cohesive failure within the fluid at an internal surface where the fluid slips on itself. We adimensionalize the drool rate with the production rate, and call this the buildup ratio, BR . We provide an exact analytical solution for BR when the cohesive slip layer either slips at the die wall, or when it does not. We examine two important extrusion geometries: slit (which we then extend to pipe) and tube flow. We identify two new experiments: one to measure BR as a function of pressure drop, and another as a function of the die aspect ratio, and we then use our new theory to design droolometers.

Polyformaldehyde (POM)/ethylene-vinyl acetate copolymer (EVA)/high-density polyethylene (HDPE) composites filled with nanometer calcium carbonate (nano-CaCO 3 ) were prepared using a twin-screw extruder. The effects of load and temperature on the melt extrudate swell behavior of the composites were investigated, by using a melt flow rate instrument under experimental conditions, with temperatures ranging from 170°C to 220°C and loads varying from 1.2 kg to 12.5 kg. The results showed that the melt die-swell ratio ( B ) of the composites decreased linearly with a rise of temperature as the load was fixed, while it increased nonlinearly with increase in the melt volume flow rate ( MVR ) and load, when the test temperature was constant; they also showed that B is a quadratic function of shear rate or shear stress. The value of B increased nonlinearly with an increase of the HDPE weight fraction ( ϕ ) as the temperature was constant, and the temperature sensitivity of B to ϕ was insignificant, while the effect of load was significant. The correlation between B and ϕ obeyed a quadratic equation.

A series of intercalated nanocomposites were prepared via in situ polymerization of 2-hydroxyethyl methacrylate (HEMA) between the interlayer spacing of hydrous Na-montmorillonite (Na-MMT) using benzoyl peroxide (Bz 2 O 2 ) as a radical initiator. X-ray diffraction patterns showed the absence of any intercalation up to 61.7 mass% of HEMA, but anhydrous Na-MMT formed by the hydrophilic effect of HEMA. The interlayer spacing ( d 001 ) values of hydrous and anhydrous Na-MMT were calculated as 1.19 and 1.03 nm, respectively. At higher monomer contents, the increase in the value of d 001 from 1.19 to 2.01 nm indicated intercalation of polymer in the interlayer spacing of Na-MMT. Besides, transmission electron microscopy results supported the formation of the intercalated nanocomposites. Thermogravimetric analysis showed that the thermal stability of the nanocomposites increased considerably by intercalation of pure poly-HEMA. Specific surface area and specific nanopore volume of the nanocomposites decreased with the increasing of the monomer content taken by the preparations. The decrease is due to the nonporous nature of the polymer matrix.

We studied the drying of polyacrylamide (PAAm)-multiwalled carbon nanotube (MWNT) composites, prepared by free radical crosslinking copolymerization in water, with a steady state fluorescence technique. Composite gels were prepared at room temperature with pyranine ( Py ) doped as a fluorescence probe. Drying experiments were performed in air at various MWNT contents by real time monitoring of the Py fluorescence intensity ( I ) which increased as the drying proceeded. The Stern-Volmer equation, combined with the moving boundary diffusion model, was used to explain the behavior of I during drying. It was observed that the desorption coefficient ( D ) increased as the temperature increased. Drying energies ( ΔE ) were measured for the drying processes for each MWNT content gel, by using fluorescence, gravimetrical and volumetric methods. It is understood that ΔE values decrease by increasing MWNT content, until 1 wt% MWNT, and then increase above the level of this threshold value. The energy of drying is strongly correlated with the MWNT content in the composite. ΔE drops to its lowest value, at which conducting cluster starts to appear.

To study the pyrolysis kinetics of exfoliated nanocomposites, polyvinyl acetate (PVAc)-montmorillonite (MMT)-dioctadecyl dimethyl ammonium bromide (DOAB) was prepared through five different synthesis processes. The synthesis processes and MMT-DOAB had some effect on the thermal degradation, which was found to consist of eight phases. MMT-DOAB had no significant effect on the pyrolysis temperature, but delayed the thermal degradation process. The pyrolysis kinetics in thermal degradation were analyzed using the Agrawal integral equation.

The morphologies of sulfonated polystyrene-block-fluorinated polyisoprene (s-PS-b-f-PI) were studied as functions of different kinds of solvents and thermal annealing, using transmission electron microscope microscopy (TEM), small angle X-ray scattering (SAXS) and intermediate angle X-ray diffraction (IMAXD). The film of the block copolymer ionomer with an acid form [sulfonated PS-b-fluorinated PI (sH-PS-b-f-PI)], which was cast from anhydrous tetrahydrofuran (THF), developed a well-ordered cylindrical morphology of the f-PI domains in the sH-PS matrix. The morphology was explained by the solubility parameter and the Bjerrum length. The morphology changed to that of a no long-range ordered structure, through thermal annealing. The result was different from the usual behavior of uncharged diblock copolymers and could have been due to the ionic cluster formation. The solution casting films of the block copolymer ionomer with a cesium neutralized form (sCs-PS-b-f-PI) were obtained from the mixed solvent of THF/water (98/2, wt/wt) and DMSO. The ionic cluster formation in the film cast from the mixed solvent was hardly changed by annealing. The promotion of the ionic cluster formation by annealing was clearly observed in the film cast from DMSO. However, hindrance of microphase separation by the promotion of the ionic cluster formation was not confirmed in this study.

Novel superabsorbent hydrogels of poly(sodium acrylate) [poly(SA)] with crude vermiculite (CVMT) and exfoliated vermiculite (EVMT) were synthesized and characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Both types of hybrids are more stable materials than poly(SA) and their thermal stability increases as the clay content increases. The equilibrium water absorbency for each hybrid type varies with the clay content, showing a maximum at 15 wt% and 20 wt% for EVMT and CVMT, respectively. The equilibrium water absorbency is higher for the hybrids than for poly(SA) at clay contents close to their maxima. The swelling kinetics obey a Voigt-based equation. The water desorption kinetics showed the existence of free water and bound water within the polymeric matrix. All of the superabsorbent materials investigated retained the water absorption capacity after repeating five wet-dry cycles.

Cation exchange membranes were prepared based on polyvinyl alcohol (PVA) and polyethersulfone (PES) polymer blends using dimethyl sulfoxide as solvent and phosphotungstic acid (PWA) as functional group agent. The membranes were fabricated by solution casting method. The effects of PVA-to-PES polymer blend ratio and PWA content on the electrochemical ion exchange properties of the prepared membranes, including fixed ion concentration (FIC), membrane potential, permselectivity, surface charge density, transport number and electrical resistance, were studied. The areal electrical resistance at room temperature was reduced by increasing the PES and decreasing the PWA contents of membranes. The results show that the addition of PWA to the membranes provides additional counterion-conducting passages and enhances the FIC, membrane potential, permselectivity and transport number.

The article presents results of a study of the effect of selected granulometric features of plastified poly(vinyl chloride) granule on the basic parameters of extrusion. In the study, it was determined how mass polymer flow rate, power supplied to the extruder, power transmitted by the polymer, unit energy consumption, and energy efficiency of the extrusion process were related to pellet length and bulk pellet density. The tests were carried out using an extruder with a screw diameter of 25 mm and a length-to-diameter ratio of 25, and involved processing of pellets of different lengths at variable rotational speeds of the screw. It was established that the granulometric features of plastified poly(vinyl chloride) considered in this study, i.e., pellet length and pellet bulk density, affect the effectiveness of the extrusion process. It was shown that best effectiveness of extrusion is achieved with the use of a granule characterized by a pellet length that is close to the other characteristic dimension of granule – its pellet diameter.

A number of polyurethane prepolymers based on polycaprolactone diol (PCL) and 4,4′-diphenyl methane diisocyanate (MDI) were synthesized and extended with different dianilines such as: 4,4′-methylenebis(2,6-diisopropylaniline) (M-DIPA), 4,4′-methylenebis(2,6diethylaniline) (M-DEA), 4,4′-methylenebis(ortho chloroaniline) (MOCA), 4,4′-methylenebis(2-isopropyl-6-methylaniline) (M-MIPA) and 4,4′-methylenebis(3-chloro-2,6-diethylaniline) (M-CDEA). Infrared (IR) spectroscopy was used to check the end of the polymerization reaction in addition to the polymer characterization. The effect of the dianiline structure on the thermal properties of the cast films were studied through dynamic mechanical measurements (DMTA), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis. It was found that the thermal properties and thermal stability of polyurethane are strongly affected by the molecular structure of the dianiline chain extender.